Process for producing soybean powder and process for poducing soybean milk

ABSTRACT

Lipoxygenase-free soybean grains are mechanically pulverized into fine particles and then subjected to heat drying treatment with water vapor having a temperature in the range of 130 to 250° C. under atmospheric pressure to form lumps of soybean powder. The lumps are formed into granules having controlled sizes by placing the lumps in a space defined by two plates having a predetermined distance therebetween and having a plurality of parallel grooves formed in the surfaces. The plates are in a state of relative rotation. This method allows the production of soybean powder free from disagreeable odor and taste and the production of soybean milk from the soybean powder, with inexpensive equipment in a quick process.

TECHNICAL FIELD

The present invention relates to methods for producing nutritioussoybean powder made from whole soybeans whose flavor and taste have beenimproved, and particularly to a novel method for producing soybeanpowder which can be used in whole-bean curd, whole-soybean milk, andtheir related products, for enriching milk, juice, and other beverages,and in new applications of soybeans, for example, to bread, noodles,cake, cookies, and chips. The dispersibility of the resulting soybeanpowder in water is enhanced so that the soybean powder can be rapidlydispersed in water or blended with other powdery food in the presence ofwater.

BACKGROUND ART

Soybeans completely lacking lipoxygenase (hereinafter referred to aslipoxygenase-free soybeans) generate almost none of the bean odorpeculiar to soybeans, and can prevent the production of lipid peroxide.The powder of lipoxygenase-free soybeans is advantageously used assoybean food material which is blended with other food material, such aswheat flour, as disclosed in, for example, Japanese Patent No. 2500350,“Method for processing soybean-processed food”. Unfortunately, soybeanscontain various types of constituents for flavor and taste irrespectiveof whether they are good or not, and source constituents of disagreeableodor and taste cannot be completely removed, even from lipoxygenase-freesoybeans.

For example, a process of soybean milk production leaves a strong taste(disagreeable taste or dry mouth feel) peculiar to raw bean curd.

Normal soybeans, not species free of lipoxygenase, generate suchdisagreeable odor and taste more strongly. Accordingly, the removal ofsuch odor and taste has been studied. Exemplary approaches include:

-   (1) physical processes, such as heat or solvent treatment;-   (2) chemical processes using a chemical agent;-   (3) processes for masking with other flavors or tastes; and-   (4) processes for separating protein.    Among these approaches, heat treatment has been widely studied    because it is relatively easy to perform. Disagreeable odors from    normal soybeans are generated mainly by oxidation of soybean lipid    induced by the enzyme activity of lipoxygenase, and the reaction    product n-hexanal or the like is probably the causative substance of    the disagreeable odor. Heat treatment is generally intended to    eliminate the activity of lipoxygenase and to remove any causative    substance that has already been produced. In this instance,    high-temperature air or high-temperature water vapor is used as a    heating medium. Special care should be taken in use of    high-temperature air because it is likely to cause lipid oxidation    and a side reaction which may brown the protein. On the other hand,    water vapor has such a high heat-transfer efficiency as to be    suitable as the heating medium.

Unfortunately, use of high-temperature water vapor of 100° C. or morerequires expensive pressure-resistant equipment and makes the operationcomplicated.

Treatment under high-pressure conditions inevitably causes water vaporto penetrate soybeans, and thus requires an additional drying step.Consequently, the price of the product increases disadvantageously.

Soybean fine powder (having a particle size, for example, betweenseveral micrometers and several hundred micrometers) thrown into waterfloats on the surface of the water without sinking below the surface,due to the high surface tension. Even if the water is forcibly stirred,the powder is divided into several lumps and the lumps keep floating. Inorder to uniformly disperse the particles of the powder (hereinafterreferred to as fine particles), stirring must be continued for a longtime.

In order to solve this problem, the powder is generally subjected togranulation, in which fine particles are bound to each other with anappropriate force and form grains (hereinafter referred to as granules)having apparently larger sizes to the extent that the grains can betreated as powder. Consequently, an indefinitely large number of voidsare formed between the fine particles except the binding sites. Thus,water coming into contact with the granules can penetrate the voids dueto capillary action, so that the granules are rapidly impregnated withthe water and sink easily.

While the granules are sinking, the appropriate bindings between thefine particles are released, so that the fine particles are uniformlydispersed to form a state that can be easily mixed with other foodmaterial.

For granulation of the powder, a variety of processes have been known,such as (1) rolling granulation, (2) extruding granulation, (3)compressing granulation, (4) pulverizing granulation, (5) stirringgranulation, (6) fluidized-bed granulation, (7) spraying granulation,(8) melting granulation, (9) coating granulation, and (10) encapsulatinggranulation.

While it goes without saying that an appropriate granulation process isselected according to the properties of the powder material and desiredproducts (granules), broadly adopted processes are performed such thatmechanical force is appropriately applied by, for example, compression,shock, or shearing so that fine particles are bound to each other toform granules, as in the processes listed above.

In granulation of soybean powder with mechanical force to form soybeangranules, oil naturally contained particularly in so-called wholesoybean powder is squeezed by applying an excessive mechanical force,which consequently impairs the properties of the powder. It is thereforenecessary to reduce the mechanical force as much as possible. This,however, undesirably provides granules having insufficient binding forcebetween fine particles and inferior shape stability. Accordingly, abinder is added to enhance the binding force. Unfortunately, the binderdegrades the purity of the resulting soybean product and may change thetaste.

In view of the above-described circumstances, the object of the presentinvention is to provide a method for producing soybean powder free fromdisagreeable odor and taste and dispersible in water in a short processwith inexpensive equipment, and a method for producing soybean milk.

DISCLOSURE OF INVENTION

A first requirement of the present invention is: (1) to uselipoxygenase-free soybeans, which inherently generate less disagreeableodor, as a raw material, and (2) to allow sufficiently high-temperaturewater vapor to act on the lipoxygenase-free soybeans under atmosphericpressure (about 1 atm) for a short time. (2) is particularly important.More specifically, the inventors investigated suitable conditions ofheat treatment for removing disagreeable odor and taste remaining in thelipoxygenase-free soybeans simultaneously with drying (together referredto as heat drying treatment) without use of pressure-resistant equipmentin spite of use of sufficiently high-temperature water vapor, whilestill inhibiting lipid oxidation and side reaction of the protein. Inthe course of this investigation, the inventors found that penetrationof water vapor into soybeans is prevented under atmospheric pressure,and that on the contrary, such water vapor treatment produces effectsdifferent from the effects by high-temperature air treatment whilepromoting drying.

In the method for producing soybean powder of the present invention,unprocessed whole soybeans are generally used as the raw materialsoybean grains, but the soybeans may each be crushed into 2 to 4 piecesin order to remove the seed coats and hypocotyls. The protein in thesoybean powder produced by this method contains water-solubleconstituents in a similar ratio to that in unheated soybean powder.Also, the extracted oil has a similar acid value and peroxide value tothat of the unheated soybean powder. In addition, the method of thepresent invention shows a large effect in removing disagreeable odor andtaste, and this effect is most notably shown in the production of wholesoybean milk and its related products.

The lipoxygenase-free soybean used herein is a species lacking all thelipoxygenases L1, L2, and L3 which are contained in normal soybeans, andregistered species “L-Star” and “Ichihime” are known in Japan. Bothspecies can be used effectively in the present invention.

The soybean powder used herein is constituted of fine particles having aweight-average particle size of about 10 to 50 μm and a maximum particlesize of about 500 μm or less, broadly including products generallycalled soybean powder.

A second requirement of the present invention is to produce tastygranules of soybean powder by the same heat drying treatment without useof special additives. More specifically, (1) soybean powder is exposedto superheated water vapor to bind fine particles to each other inadvance, and then (2) the binding is partially released by applying aweak shearing force by use of opposing flat plates with a spacetherebetween.

The inventors have studied granulation as well as heat denaturation ofsoybean protein in order to improve the taste of soybean powder. In thecourse of this study, the inventors found that superheated water vaporcauses the fine particles of soybean powder to bind into larger lumps,and that when the lumps are placed in water, they rapidly sink and thebindings between the particles are released so that the particles areuniformly dispersed.

Since the lumps produced by the superheated water vapor have varioussizes, they cannot be used as powder. It is therefore necessary toreprocess the lumps into granules having similar sizes. In the presentinvention, the lumps are pulverized into appropriate sizes, and then ashearing force is applied to the material placed between two opposingplates, at least one of which has grooves. Thus, similar-size granulesare produced without squeezing oil out, and in which the bindingsbetween the fine particles are partially released. The resultinggranules exhibit superior dispersibility in water. The set of platesused herein refers to means having a structure in which the regionbetween the opposing plates maintains a predetermined distance; hence,the set of plates may be a thick structure, such as a mortar.

In the granules of soybean powder produced by the method of the presentinvention, most of the protein has been denatured and physiologicallyharmful substances in the soybeans have been completely inactivated. Thegranules may therefore be added to beverages, such as milk, juice, soup,and sauce, to be ingested without being heated.

The processes described in the first and second requirements performheat drying treatment by contact with sufficiently high-temperaturewater vapor. The sufficiently high-temperature water vapor is producedby reheating water vapor from boiling water of 100° C. under atmosphericpressure, and generally has a temperature in the range of 130 to 250° C.For the reheating, it is advantageous to use a metal plate heated byelectromagnetic induction as a heat source from the viewpoint of ease oftemperature control. The resulting high-temperature, normal-pressurewater vapor is introduced into a heat-maintaining container and used asa heating medium for the heat drying treatment. The heat dryingtreatment time is set in the range of 30 to 300 seconds. It goes withoutsaying that heat drying treatment at an excessively low temperature orfor an excessively short time leads to unsatisfactory results, and thattreatment at an excessively high temperature or for an excessively longtime can cause undesired side reactions. Consequently, such conditionshinder the production of satisfactory products.

In order to apply the present invention effectively, it is preferablethat the treatment is generally performed at a sufficiently hightemperature much beyond 100° C. for a shorter time. More specifically, amore preferred temperature is in the range of 160 to 230° C., and a morepreferred time is in the range of 60 to 180 seconds.

Since the soybean grains in the first requirement and the fine powder inthe second requirement after the heat drying treatment do not containwater vapor, and are, on the contrary, well dried, they can be sent to apulverization or granulation step immediately after cooling.Pulverization is performed on the soybean grains by applying mechanicalforce, such as compressing force, impact force, or shearing force. Inthis instance, special care needs to be taken to prevent lipid (oil)separation and lipid oxidation and deterioration. Preferably,compressing force is avoided from the viewpoint of preventing lipidseparation. In use of impact force and shearing force, lipid oxidationand degradation resulting from an increase in temperature must beprevented. According to the experience of the present inventors, arotating mortar mainly using shearing force, equipped with a coolingmechanism can provide sufficiently fine and high-quality powder.

The apparatus for forming granules is also based on the principle of therotating mortar. In the present invention, two plates having grooves intheir surfaces (opposing surfaces of the mortar) are disposed at apredetermined distance without contacting each other. One of the platesis rotated (or is allowed to stand in a state of relative rotation by,for example, varying the rotational speeds of the two plates) to apply ashearing force to the lumps between the plates. The shearing force canbe controlled by varying the distance between and the rotational speedsof the plates. The size of the granules mainly and greatly depends onthe distance between the opposing plates, and also depends on themagnitude of the shearing force and the depth and pitch of the grooves.In general, the depth of the grooves is in the range of 0.20 to 0.25 mmand the pitch is in the range of 1.5 to 2.5 mm. The grooves provided ina mortar are used as passages for transmitting the shearing force anddischarging the granules.

Thus, the present invention changes the properties of soybean powdersimply by varying the form of the raw material without varying heatdrying temperature or time. The soybean powder produced by the method ofthe present invention can be broadly used as nutritionally balanced foodmaterial in fields where soybeans have been hardly used, for example, inthe fields of production of bread, noodles, cake, cookies, and chips.

In the method for producing soybean milk of the present invention,soybean milk is produced from the soybean powder produced by the methodof the present invention. In particular, the granules of the soybeanpowder can be ingested as soybean milk free from disagreeable odor andtaste simply by being dissolved in water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an apparatus used for heat drying treatmentof soybean powder according to the present invention.

FIG. 2 is a perspective view of a mortar according to the presentinvention.

FIG. 3 is a representation of a state where the upper mortar member andthe lower mortar member shown in FIG. 2 are combined.

FIG. 4 is a plan view of the lower mortar member.

FIG. 5 is a bottom view of an upper mortar member.

FIG. 6 is an enlarged view of portion A shown in FIG. 2.

FIG. 7 is a chart of the particle size distribution of raw materialsoybean powder dispersed in ethanol.

FIG. 8 is a chart of the particle size distribution of raw materialsoybean powder dispersed in air.

FIG. 9 is a chart of the particle size distribution after granulation.

FIG. 10 is a chart of the particle size distribution after granulationin which the space of the mortar is set larger than that in FIG. 9.

BEST MODE FOR CARRYING OUT THE INVENTION

Heat drying treatment according to an embodiment of the presentinvention will now be described. FIG. 1 shows the structure of anapparatus 20 used for heat drying treatment. Superheated water vaporherein refers to unsaturated water vapor exhibiting high drying abilityproduced by, for example, reheating saturated water vapor generated froma boiler 1 in a water vapor heater 2. The superheated water vapor has atemperature in the range of 130 to 230° C. For the reheating of thesaturated water vapor, it is advantageous in terms of temperaturecontrol to use a metal plate heated by electromagnetic induction as aheat source. Use of Water vapor of a saturated or a supersaturated typewith low drying ability causes excessive water to penetrate the rawmaterial during the treatment, consequently requiring a drying step.Particularly in granulation, a strong binding force is eventuallygenerated between the fine particles, accordingly reducing thedispersibility in water of the fine particles after granulation.

The superheated water vapor is introduced into a reservoir 4 through asuperheated water vapor pipe 3, and further transmitted into aprocessing portion 5 through holes in a plate to come into contact withthe raw material. The spent superheated water vapor is discharged out ofthe apparatus through water vapor outlets 7. Preferably, the treatmenttime is appropriately selected in the range of 30 to 300 seconds. Itgoes without saying that treatment at an excessively low temperature orfor an excessively short time lead to unsatisfactory results, and thattreatment at an excessively high temperature or for an excessively longtime can cause undesired side reactions. Consequently, such conditionshinder the production of satisfactory products. In order to apply thepresent invention effectively, it is preferable that the treatment begenerally performed at a sufficiently high temperature much beyond 100°C. for a shorter time. More specifically, a more preferred temperatureis in the range of 160 to 190° C., and a more preferred time is in therange of 60 to 180 seconds.

The treatment with the apparatus shown in FIG. 1 is performed underatmospheric pressure, that is, under a condition with an extremely smalldifference in pressure between the outside and inside of the apparatus.It is therefore necessary to take particular care not to retain thewater vapor in the apparatus. In particular, the reservoir 4 is liableto cause such retention. If the temperature decreases while the watervapor remains, the drying ability is degraded. This is must beprevented. In order to induce a flow so as to prevent retention, forexample, water vapor is forcibly discharged. The water vapor outlets 6of the apparatus shown in FIG. 1 are based on a so-called naturalchimney effect, and are each an enforced system equipped with amotorized exhaust fan to ensure the chimney effect.

The treatment with the open-type apparatus is suitable to continuouslyperform production steps. Specifically, the raw material placed on aconveyer 8 from a raw material feed table 7 is subjected to thetreatment while being conveyed, and then cooled down on a productreceiving table 9. Water vapor does not penetrate the product. If theraw material is of fine particles, the particles bind to each other toform lumps.

The heat drying treatment of soybean grains or soybean powder has beendescribed. Subsequently, granulation of soybean powder will now bedescribed.

For granulation of soybean powder to form granules, fine particles ofsoybeans are supplied as the raw material to the apparatus 20. The fineparticles are prepared with a mortar 10 shown in FIG. 2.

The mortar 10 includes an upper mortar member 11 and a lower mortarmember 12. The lower mortar member 12 includes a portion having parallelgrooves 13 and a portion having protrusions 14.

FIG. 3 shows the state where the upper mortar member 11 covers the lowermortar member 12. The upper mortar member 11 is indicated by dottedlines. The mortar also includes a rotation driver, which is not shown.

FIG. 4 is a plan view of the lower mortar member 12. The lower mortarmember 12 includes a plurality of segments (B) having parallel grooves13. FIG. 5 is a bottom view of the upper mortar member 11. The uppermortar member 11 also includes a plurality of segments 13 havingparallel grooves in the same manner as in lower mortar member 12.However, the upper mortar member and the lower mortar member havedifferent groove angles with respect to the axis.

FIG. 6 is an enlarged view of portion A shown in FIG. 2. The grooves areformed at a depth (H) of about 0.25 mm and at a pitch (L2) of about 2.0mm.

The lumps produced by the heat drying treatment are placed in the mortar10, and the upper mortar member 11 and the lower mortar member 12 arerotated with a predetermined distance L maintained therebetween. Thedistance L is set depending on the size of the granules to be produced.In general, the distance is between several tens of micrometers andseveral millimeters, but is not limited to this range.

Thus, soybean granular powder is produced by the granulation (step).

<Examples of the Water Dispersibility of Soybean Powder>

COMPARATIVE EXAMPLE 1

The particle size distribution of the raw material soybean powder wasmeasured. FIG. 7 shows the results of measurement in which the soybeanpowder was dispersed in ethanol, and FIG. 8 shows the results ofmeasurement in which the soybean powder was dispersed in air. Thedispersion in ethanol provided substantially a single distributionstructure exhibiting a large peak at a particle size of about 22 μm. Onthe other hand, the dispersion in air provided a plurality ofdistribution structures exhibiting their respective peaks at 55 μm, 185μm, and 517 μm; the distribution structures seemed to overlap with oneanother. Apparently, these results suggest that the fine particles ofsoybean powder are present separately and independently in ethanol, andthat, in air, a plurality of fine particles bind to form grains and thegrains further bind to each other.

EXAMPLES 1 AND 2

The raw material soybean powder of the same lot as that used in theComparative Example was formed into lumps by applying superheated watervapor at 190° C. for 180 seconds. The lumps were granulated with adifferent distance (L) between the opposing mortar members. Theresulting granules were dispersed in air and the particle sizedistribution was measured. The results are shown in FIG. 9 (Example 1)and FIG. 10 (Example 2). Example 1 was performed with a smaller distancebetween the opposing mortar members; Example 2, with a larger distance.Both cases simplified the multiple particle size distribution into asingle peak distribution. The peak particle size in Example 1 was about7 times as large as that in ethanol (see FIG. 7), and the peak particlesize in Example 2 was 15 times. This suggests that granulation wascarried out effectively.

COMPARATIVE EXAMPLE 2 AND EXAMPLES 3 AND 4

One gram of each of the raw material soybean powder and granulesproduced in Example 1 or 2 was placed in water, and the time needed forthe powder or granules to sink completely was measured. The raw materialsoybean powder was partially repelled from the water and remained on thesurface of the water even after 5 minutes had elapsed (ComparativeExample 2). On the other hand, the samples granulated in Examples 1 and2 sank completely within 10 seconds (Examples 3 and 4, respectively).These results clearly show that granules produced by the method of thepresent invention have superior hydrophilicity.

<Examples of Tastes of Soybean Powder and Soybean Milk>

The present invention will be further described in detail with referenceto a comparative example and examples, but the scope of the invention isnot limited to these examples.

Soybean powders produced by the following three processes were subjectedto evaluation tests.

First Production Process

Lipoxygenase-free soybean grains or crushed grains were subjected toheat drying treatment with water vapor of a temperature in the range of130 to 250° C. under atmospheric pressure, and were then mechanicallypulverized into fine particles.

Second Production Process

Lipoxygenase-free soybean grains were mechanically pulverized into fineparticles, and then subjected to heat drying treatment with water vaporof a temperature in the range of 130 to 250° C. under atmosphericpressure.

Third Production Process

Lipoxygenase-free soybean grains were mechanically pulverized into fineparticles, then subjected to heat drying treatment with water vapor of atemperature in the range of 130 to 250° C. under atmospheric pressure,and further granulated by placing the lumps of soybean powder formed byoverheat drying treatment in the space between the opposing mortarmembers.

EXAMPLES NO. 1 TO No. 5

Soybean (L-Star) powder produced by the first production process wasimmersed in water and allowed to stand until the soybean powdersufficiently absorbed the water (for about 16 hours). The weight ofwater was about 10 relative to the weight of the soybean powder. Then,the sample was filtered through cloth and heat-treated in a hot waterbath for 30 minutes to yield soybean milk.

Table 1 shows heat drying conditions for lipoxygenase-free soybeanpowder. Five samples No. 1 to No. 5 were used. For a comparativeexample, fine powder of lipoxygenase-free soybean grains not subjectedto heat drying treatment was used. TABLE 1 Heat Drying Conditions forSoybean Grains Comparative Examples Conditions Example No. 1 No. 2 No. 3No. 4 No. 5 Temperature (° C.) untreated 150 170 170 170 200 Time (s)120 60 90 120 60

The tastes of the resulting soybean milk samples were subjected toevaluation tests by questionnaires. Ten each of adult men and women,namely 20 people in total, were randomly selected. Table 2 showsevaluation items, criteria, and average score by the 20 people.According to this table, although all the samples used the samelipoxygenase-free soybeans, each of the soybean milk samples preparedfrom the soybean powder of the present invention received higher scoresthan the soybean milk of the comparative example. The results of thetaste evaluation of the soybean milk samples are shown in Table 2. TABLE2 Taste Evaluation of Soybean Milk Evaluation item, evaluation pointComparative Soybean milk sample score Example No. 1 No. 2 No. 3 No. 4No. 5 Bean odor 1. Largely remaining 3.2 4.5 4.7 4.7 4.6 4.5 2. Littleremaining 3. Slightly remaining 4. Hardly remaining 5. Completelyremoved Taste 1. Bad 2.5 4.2 4.5 4.6 4.3 4.2 2. Rather bad 3. Fair 4.Rather good 5. Good Comprehensive 1. Bad 2.2 4.2 4.5 4.6 4.3 4.2evaluation 2. Rather bad 3. Fair 4. Rather good 5. GoodScore = total evaluation points/number of testers

EXAMPLES NO. 6 AND NO. 7

A soybean powder sample of Example No. 6 was prepared by the firstproduction process at a heat drying temperature of 170° C. for 90seconds, and a soybean powder sample of Example No. 7 was prepared bythe second production process at a heat drying temperature of 230° C.for 90 seconds. A soybean powder sample not subjected to heat dryingtreatment was used for a comparative example. The acid value andperoxide value of oil extracted from each sample were measured.

Table 3 shows how the heat drying treatment affects the acid value andperoxide value. According to Table 3, it is obvious that the processesof the present examples do not change the acid value and peroxide valueeven though heat drying treatment is applied. TABLE 3 Effect of HeatDrying Treatment on Acid Value and Peroxide Value Soybean grain sampleComparative Evaluation item Example No. 6 No. 7 Acid value 2.33 1.522.74 Peroxide value 0.6 meq/kg 0.4 meq/kg 0.5 meq/kg

EXAMPLES NO. 8 TO NO. 10

The sample of Example No. 6 produced by the first production process wasused in Example No. 8, and the sample of Example No. 7 produced by thesecond production process was used in Example No. 9. In addition, asoybean powder sample prepared by heat drying treatment at a temperatureof 170° C. for 120 seconds was used in Example No. 10.

For a comparative example, a soybean powder sample not subjected to heatdrying treatment was used. The trypsin inhibitor activity of each samplewas measured and the results are shown in Table 4. The trypsin inhibitoractivity in the comparative example was 57.8 TIU/mg.

The results clearly show that while the soybean powder produced by thefirst production process is still rawish, the soybean powder produced bythe second production process exhibits low trypsin inhibitor activityand is very edible. TABLE 4 Results of Trypsin Inhibitor ActivityMeasurement Soybean grain sample Evaluation item No. 8 No. 9 No. 10Trypsin inhibitor activity 34.4 TIU/mg 20.4 TIU/mg 21.5 TIU/mg

EXAMPLES NO. 11 TO NO. 14

Soybean powder samples were prepared by the third production processunder the conditions shown in the table below. For a comparativeexample, lipoxygenase-containing normal soybeans (species: Fukuyutaka)were used as the raw material. On the other hand, lipoxygenase-freesoybeans (species: L-Star) were used for the examples. Each raw materialwas pulverized into fine particles having an average particle size ofabout 15 μm and a maximum particle size of about 108 μm, and water vaporof a temperature shown in the table below was applied to the particlesunder normal pressure for a time shown in the same table. Then,granulation was performed to adjust the particle size. The resultinggranules were used for evaluation. TABLE 5 Conditions for Soybean PowderProduction Example Treatment Comparative Example No. No. No. No.conditions a b c d e f 11 12 13 14 Temperature 130 150 170 190 230 190(° C.) Time 180 90 180 150 180 210 240 (s)

The bean odor and disagreeable taste intensities of the resultingsoybean powder sample were measured by directly placing the sample inthe mouth. The results are shown in Tables 6 and 7. Since thecomparative examples (Table 6) were not able to remove disagreeabletaste completely as well as the bean odor, most of their comprehensiveevaluations were bad or rather bad (“f” was for reference and generateda strong flavor of soybean flour). In contrast, Examples (Table 7)according to the present invention did not leave disagreeable taste, andmost of their comprehensive evaluations were rather good or good. TABLE6 Taste Evaluation Results of Removal of Bean Odor and DisagreeableTaste Evaluation item, evaluation point Comparative Example Sample scorea b c d e f Bean odor 1. Largely remaining 2.0 1.5 1.5 2.3 1.0 3.5Comprehensive Bad evaluation 2. Little remaining Rather bad 3. Slightlyremaining Fair 4. Hardly remaining Rather good 5. Completely removedGoodScore = total evaluation points/number of testers

TABLE 7 Taste Evaluation Results of Removal of Bean Odor andDisagreeable Taste Evaluation item, evaluation point Example Samplescore No. 11 No. 12 No. 13 No. 14 Bean odor 1. Largely remaining 4.0 5.05.0 4.8 Comprehensive Bad evaluation 2. Little remaining Rather bad 3.Slightly remaining Fair 4. Hardly remaining Rather good 5. Completelyremoved GoodScore = total evaluation points/number of testers

In the embodiment of the present invention, lumps produced by heatdrying treatment are granulated by being placed in a mortar forproducing fine particles, with the mortar space adjusted. Thus,water-dispersible granules of soybean powder are produced without use ofany binder. Therefore, use of lipoxygenase-free soybean grains as theraw material results in soybean powder free from disagreeable odor andtaste, suitable for cooking, and whose taste has not been degraded bythe binder.

INDUSTRIAL APPLICABILITY

As described above, the present invention can efficiently producesoybean powder having less disagreeable odor and taste. In addition,soybean milk having less disagreeable odor and taste can be producedfrom this soybean powder.

Furthermore, the process for granulating soybean powder of the presentinvention does not need any additive to remain and is easy to perform.The resulting granules have a single particle size distributionstructure and superior hydrophilicity, and accordingly can easilydisperse in water.

1. A method for producing soybean powder, comprising the steps of:subjecting grains or crushed grains of lipoxygenase-free soybeans toheat drying treatment with water vapor having a temperature in the rangeof 130 to 250° C. under atmospheric pressure; and then mechanicallypulverizing the grains into fine particles.
 2. A method for producingsoybean powder, comprising the steps of: mechanically pulverizinglipoxygenase-free soybean grains into fine particles; and thensubjecting the fine particles to heat drying treatment with water vaporhaving a temperature in the range of 130 to 250° C. under atmosphericpressure.
 3. A method for producing soybean powder, comprising the stepsof: mechanically pulverizing lipoxygenase-free soybean grains into fineparticles; subsequently subjecting the fine particles to heat dryingtreatment with water vapor having a temperature in the range of 130 to250° C. under atmospheric pressure to form lumps of soybean powder; andthen forming granules having controlled sizes by placing the lumps in aspace defined by two opposing plates having a predetermined distancetherebetween, at least one of the plates having a plurality ofsubstantially parallel grooves in the surface thereof, the plates beingin a state of relative rotation.
 4. The method for producing soybeanpowder according to claim 1, wherein the heat drying treatment isperformed for a time in the range of 30 to 300 seconds.
 5. The methodfor producing soybean powder, wherein soybean milk is made from thesoybean powder produced by the method as set forth in claim
 1. 6. Amethod for producing soybean powder, comprising the step of forminggranules having controlled sizes by placing a soybean powder materialwhich has been processed into lumps by use of superheated water vapor,in a space defined by two opposing plates having a predetermineddistance therebetween, the two plates having a plurality of parallelgrooves in the surface thereof, at least one of the two plates beingrotated.
 7. The method for producing soybean powder according to claim6, wherein the grooves have a pitch of 1.5 to 2.5 mm and a depth of 0.20to 2.5 mm.